The present invention relates to perfluoropolyether lubricants having pendent sulphonylfluoride groups distributed from the polymeric backbone.
Specifically the invention relates to lubricants having an improved glass transition temperature (Tg) (up to xe2x88x92130xc2x0 C.) combined with a high thermo-oxidative stability and obtainable by a process having improved Productivity with respect to the known lubricant process.
More specifically, the invention relates to lubricants based on perfluoropolyethers (PFPE) which, compared with the known commercial products in the lubricant field, show the following combination of properties:
Tg in the range from xe2x88x92130xc2x0 to xe2x88x9260xc2x0 C.;
Tg adjustable in function of the monomeric units present in the polymeric backbone, adjustable also when the molecular weight is the same;
high thermal stability also in oxidative conditions;
obtainable by a process in high productivity.
The preparation of perfluoropolyethers formed of oxyperfluoroalkylene sequences containing peroxidic groups in various amounts depending on the reaction conditions, is known in the prior art. These compounds can be obtained by oxidation of perfluoroolefins at low temperature (between xe2x88x92100xc2x0 C. and xe2x88x9230xc2x0 C.) with oxygen in the presence of UV radiations, or alternatively, by oxidation of perfluoroolefins at low temperature with oxygen in the presence of suitable polymerization initiators, for example F2, CF3OF. See EP 393,700 and EP 654,493. The elimination of the peroxidic groups from the perfluoropolyether chain can be carried out both by thermal and photochemical route. In these patents perfluoropolyethers having pendent functional groups from the polymeric backbone are not described.
Perfluoropolyethers having pendent functional groups from the polymeric backbone are described in EP 244,839. It is described the photooxidation of perfluorobutadiene, optionally with a perfluorinated olefin at low temperature in the presence of oxygen and subsequent photochemical decomposition of the peroxidic groups, allowing to obtain perfluoropolyethers formed by a backbone of oxyperfluoroalkylene units with pendent fluorinated epoxide groups. By converting the fluorinated epoxide groups polyfunctional derivatives having functional groups such as xe2x80x94COOH, xe2x80x94COOR, xe2x80x94CONHR (Rxe2x95x90H or C1-C12 alkyl), xe2x80x94CN, xe2x80x94CH2OH, xe2x80x94CH2NH2, etc. can be obtained which can be used for various applications depending on the functional groups pending along the polymeric backbone. The drawback of this patent is that the functional derivatives are obtained by complex reactions which require intermediate steps.
In U.S. Pat. No. 4,384,128 copolymers obtained from hexafluoropropene oxide (HFPO) and from perfluoroglycidyl-ethers epoxides, according to the following polymerization reaction, are described: 
wherein: Rf is selected from xe2x80x94CF2CF2SO2F, xe2x80x94(CF2)4COF, xe2x80x94CF2CF2CN, xe2x80x94C6F5, xe2x80x94CF2CF(CF3)OCF2CN, xe2x80x94CF2CF2OC6F5.
The polymerization carried out in the presence of a suitable solvent and anionic initiators at a temperature in the range xe2x88x9235xc2x0 C. and 0xc2x0 C. allows to obtain non peroxidic perfluoropolyethers. Subsequently, the copolymers contining the functional groups xe2x80x94COF, xe2x80x94COOH, xe2x80x94SO2F, reacted with suitable reactants can be converted into functionalized polymers containing the xe2x80x94COCl, xe2x80x94CONH2, xe2x80x94SO2OH, xe2x80x94SO2OMxe2x80x2, xe2x80x94CO2Mxe2x80x2, xe2x80x94CN groups, wherein Mxe2x80x2 is an alkaline metal or an ammonium group, which are endowed with hydrophilicity and have ionic exchange properties. The patent aim is the curing of these polymers in order to obtain moldable articles.
The use of PFPEs as lubricants is furthermore known, for example FOMBLIN(copyright) Y commercialized by AUSIMONT, having the following structure:
CF3xe2x80x94(Oxe2x80x94CF(CF3)xe2x80x94CF2)mxe2x80x94(Oxe2x80x94CFY)nxe2x80x94Oxe2x80x94CF3xe2x80x83xe2x80x83(I)
wherein Yxe2x95x90F, CF3 and the m/n ratio ranges from 5 to 40.
The Tg values obtained with these PFPEs are of the order xe2x88x9265xc2x0 C.-85xc2x0 C. and depends on the PFPE number average molecular weight. The molecular weight being fixed, the Tg has a well determined value. Therefore the only way to furtherly decrease the Tg is to reduce the molecular weight. This implies products having high vapour pressure. They have the drawback to require frequent lubricant re-fillings since there are substantial losses of product in the use at high temperatures. This phenomenon is even more evident in specific applications, for example in aerospace field, wherein the lubricant is used in temperature cycles varying from very high temperature values to very low temperature values.
To overcome this drawback, an alternative is the use of FOMBLIN(copyright) Z commercialized by AUSIMONT, having the following structure:
CF3xe2x80x94(Oxe2x80x94CF2xe2x80x94CF2)mxe2x80x94(Oxe2x80x94CF2)nxe2x80x94Oxe2x80x94CF3xe2x80x83xe2x80x83(II)
wherein the m/n ratio ranges from 0.3 to 5.
The Tg obtained with these PFPEs are of the order of xe2x88x92130xc2x0 C. and xe2x88x92120xc2x0 C. and depend on the PFPE number average molecular weight and on the m/n ratio.
The perfluoropolyether FOMBLIN(copyright) Z have however the drawback to be obtained with a process having low productivity. In fact for their obtainment it is necessary to polymerize the tetrafluoroethylene monomer in the presence of a solvent. This involves a high production cost of FOMBLIN(copyright) Z compared with that of FOMBLIN(copyright) Y. Furthermore FOMBLIN(copyright) Z compared with FOMBLIN(copyright) Y shows a reduced thermal stability in oxidative conditions.
The need was felt to have available a perfluoropolyether lubricant overcoming the drawbacks of commercial products.
The Applicant has surprisingly and unexpectedly found a class of lubricants which solves the above technical problem showing the following combination of properties:
Tg in the range xe2x88x92130xc2x0 and xe2x88x9260xc2x0 C.;
Tg adjustable in function of the monomeric units present in the polymeric backbone, adjustable also when the molecular weight is the same;
high thermal stability also in oxidative conditions;
obtainable by a process in high productivity.
An object of the invention are perfluoropolyether lubricants containing sequences of oxyperfluoroalkylene units, characterized by the presence of sulphonylfluoride groups pending from the polymeric backbone and having the following formula (III): 
wherein:
T are end groups selected from xe2x80x94CF2X (Xxe2x95x90F,CF3,Cl), xe2x80x94C3F7, xe2x80x94COF, xe2x80x94CF(CF3)COF, xe2x80x94CF2COF, xe2x80x94CF2COCF3;
d,e,f,h are integers; a,b,c can be zero or integers; said units are statistically distributed along the chain, being a+b+c+d+e+f+h such that the number average molecular weight ranges from 500 to 5xc3x97105, preferably from 1,000 to 50,000.
Generally the units d,e,f,h are present in most polymeric chains; of course some chains can contain only some of these units.
The perfluoropolyether lubricants of the invention are homopolymers of the perfluoro 3-oxa 5-fluorosulphonyl 1-pentene (CF2xe2x95x90CFOCF2CF2SO2F) or copolymers of this sulphonic monomer with perfluoroolefins.
The perfluoroolefins are preferably tetrafluoroethylene and/or perfluoropropene.
Other optional units which can be present are those derived from comonomers, such as for example perfluoroal-kylvinylethers CF2xe2x95x90CF2ORf, wherein Rf is a perfluoroalkyl group xe2x80x94CF3, xe2x80x94C2F5, xe2x80x94C3F7, or perfluorinated conjugated dienes, in particular perfluorobutadiene.
The perfluoropolyether lubricants of the present invention can therefore contain perfluorinated units of the type xe2x80x94(CF2CF(CF3)O)xe2x80x94, xe2x80x94(CF(CF3)O)xe2x80x94, xe2x80x94(CF2CF2O)xe2x80x94, xe2x80x94(CF2O)xe2x80x94, xe2x80x94(CF2CF(OCF2CF2SO2F)O)xe2x80x94, xe2x80x94(CF(OCF2CF2SO2F)O)xe2x80x94 statistically distributed along the chain and in an amount variable depending on the operating conditions.
The sulphonic functional perfluoropolyethers of the invention contain in variable amounts, depending on the operating polymerization process conditions, the above units. Besides the sulphonic pendent group is linked to the backbone through an oxygen atom (Cxe2x80x94Oxe2x80x94C bond). According to a not binding theory, the Applicant considers that these structural characteristics bring a greater flexibility degree and therefore a greater conformational freedom to the chain and to the pendent groups having the reactive function, with consequent decrease of the invention PFPE Tg with respect to the PFPEs of the prior art, the molecular weight being equal.
The products of the present invention, due to their particular structure and to the possibility to change the ratios of the units present in the structure depending on the operating conditions, show a glass transition temperature Tg in the range xe2x88x92130xc2x0 C. and xe2x88x9260xc2x0 C. and have a good oxidative stability also at high temperatures wherefore they can be used in a wide temperature range in various applications.
The lubricants of the invention in comparison with the commercial lubricants FOMBLIN(copyright) Y show a lower Tg, the molecular weight being equal, since it is possible to change their structure without the need to lower the molecular weight, which would involve an increase of the vapour pressure with the above drawbacks.
Besides the lubricants of the invention even though they maintain a high thermo-oxidative stability, show Tg values down to xe2x88x92130xc2x0 C. which in the prior art are obtainable only with FOMBLIN(copyright) Z, which have however the above drawbacks.
The Applicant has surprisingly found that it is possible to furtherly lower the Tg until reaching also the values of FOMBLIN(copyright) Z when the xe2x80x94CF2CF2Oxe2x80x94 units having two carbon atoms are also present. Unexpectedly it has been found that the units with the SO2F group even though they have pending groups as the xe2x80x94CF2CF(CF3)Oxe2x80x94 units having three carbon atoms of FOMBLIN(copyright) Y, do not cause a Tg increase.
As known, the thermo-oxidative stability of FOMBLIN(copyright) Z is lower than that of FOMBLIN(copyright) Y. The thermal stability of the lubricants of the invention also when they contain the xe2x80x94Cxe2x80x94CF2CF2Oxe2x80x94 units having two carbon atoms, characteristic units of FOMBLIN(copyright) Z, is very high and substantially comparable with that of FOMBLIN(copyright) Y.
When tetrafluoroethylene (CF2xe2x95x90CF2) is used as comonomer of perfluoro 3-oxa 5-fluorosulphonyl 1-pentene (CF2xe2x95x90CFOCF2CF2SO2F), the perfluoropolyether lubricant of the present invention has the following structure: 
wherein:
T are end groups selected from xe2x80x94CF2X (Xxe2x95x90F,CF3,Cl), xe2x80x94COF, xe2x80x94CF2COF;
c,d,e,f,h have the above defined meaning with the proviso that c cannot be equal to 0.
When hexafluoropropene (CF2xe2x95x90CFxe2x80x94CF3) is used as comonomer, a perfluoropolyether of the following structure is obtained: 
wherein:
T are end groups selected from xe2x80x94CF2X (Xxe2x95x90F,CF3), xe2x80x94C3F7, xe2x80x94COF, xe2x80x94CF2COF, xe2x80x94CF(CF3)COF, xe2x80x94CF2COCF3;
a,b,d,e,f,h have the above defined meaning with the proviso that a,b cannot be 0.
When CF2xe2x95x90CFOCF2CF2SO2 is copolymerized with a mixture of tetrafluoroethylene and perfluoropropene, the products of general formula (III) are obtained, with the proviso that a,b,c are different from zero.
When CF2xe2x95x90CFOCF2CF2SO2F is homopolymerized, a PFPE of the following structure is obtained: 
wherein:
T are end groups selected from xe2x80x94CF2X (Xxe2x95x90F,CF3,Cl), xe2x80x94COF, xe2x80x94CF2COF, xe2x80x94CF2CF2SO2F;
d,e,f,h have the above defined meaning.
The homopolymers can have a very high number of pendent sulphonic groups, not obtainable with any other synthesis method known so far.
The perfluoropolyethers of the invention can be obtained starting from the above mentioned monomers by a photooxidation process, i.e. a polymerization process in the presence of oxygen which utilizes the action of ultraviolet radiations; or by an alternative process which excludes the use of ultraviolet radiations and uses compounds having the function of polymerization initiators, or by a mixed process which uses UV radiations and polymerization initiators as defined hereunder.
In the former case the perfluoro 3-oxa 5-fluorosulphonyl 1-pentene (CF2xe2x95x90CFOCF2CF2SO2F) monomer, optionally perfluorinated olefins, are contemporaneously fed with an O2 flow in a liquid reaction mixture formed of a solvent selected from chlorofluorocarbons (CFC), hydrochlorofluorocarbons (HCFC), hydrofluorocarbons (HFC), fluoroethers (FE), hydrofluoroethers (HFE), fluorocarbons (FC) or mixtures thereof. In the case of the copolymerization with hexafluoropropene (HFP) one usually operates in absence of solvent. During the polymerization, the liquid reaction medium is maintained at a temperature in the range xe2x88x92100xc2x0 and +50xc2x0 C., preferably xe2x88x9290xc2x0 and xe2x88x9230xc2x0 C., and irradiated with ultraviolet radiation having a wave length in the range 2,000-6,000 Axc2x0.
In the latter case the CF2xe2x95x90CFOCF2CF2SO2F monomer, optionally perfluorinated olefins, in the case of copolymerization, are contemporaneously fed with an O2 flow in a liquid reaction medium formed of a solvent selected from the above mentioned compounds. In the liquid reaction medium, kept at a temperature in the range xe2x88x92100xc2x0 and +50xc2x0C., preferably xe2x88x9290xc2x0 and xe2x88x9230xc2x0 C., a gaseous or liquid flow of one or more compounds having one or more F-Q bonds wherein Q is selected between fluorine and oxygen, is fed; when Q is oxygen, the initiator is an organic compound containing one or more fluoroxy groups. Commonly the initiator is a FORf compound wherein Rf is a perfluoroalkyl radical having from 1 to 3 carbon atoms; or it is a compound of the FOCF2OF, OFxe2x80x94(RO)sxe2x80x94F, Rfxe2x80x94(RO)sxe2x80x94F type with R perfluoroalkylene radical of the xe2x80x94CF2xe2x80x94, xe2x80x94CF2CF2xe2x80x94, xe2x80x94CF2CF(CF3)xe2x80x94 type, wherein s is in the range 1-100. Said initiators are described in U.S. Pat. Nos. 5,142,842, 5,258,110, 5,488,181. The initiator flow-rate is adjusted so that the molar ratio between the initiator and the monomers in the reaction medium is in the range 0.0001-0.1.
In the mixed process it is used the process of the latter case in the presence of UV radiations.
In the processes of the invention oxygen is fed into the reactor, the partial oxygen pressure is generally in the range 0.01-15 atmospheres; the concentration of the CF2xe2x95x90CFOCF2CF2SO2F monomer is generally comprised between 0.001 mole/litre and its molar concentration at the pure state. By molar concentration at the pure state, it is meant that the polymerization can be carried in the presence of the sulphonic monomer at the liquid state, or the maximum concentration of said monomer in the above mentioned used solvent. The man skilled in the art is easily able to determine said maximum concentration.
The reaction can be carried out in batch or in a continuous way, continuously drawing from the reactor an aliquot of the liquid phase, subjecting it to distillation, recycling the solvent, if any, and the unreacted monomers and recovering the reaction product.
In the case of copolymers, the frequency of the sulphonylfluoride group xe2x80x94CF(OCF2CF2SO2F)xe2x80x94 in the chain is proportional to the perfluoroalkylsulphonyl-vinylether/(olefins++optional comonomers) ratio in the reaction mixture and it can range from 1 to 99% of the total units of the perfluoropolyether.
From the above mentioned polymerization techniques perfluoropolyethers containing in the chain peroxidic groups, are obtained.
The peroxidic bond scission brings to the formation of functionalized end groups, making available perfluoropolyether structures having mono and bifunctional end groups of the xe2x80x94COR (Rxe2x95x90F, xe2x80x94OH, xe2x80x94OCH3, xe2x80x94OC2H5, xe2x80x94OC3H7) type, or of the xe2x80x94OCF2Y (Yxe2x95x90Br,I) type and containing along the backbone pendent sulphonic groups. This is a further advantage of the products of the invention, since polycondensation polymers can be prepared by using the above mentioned end groups. Said scission processes are described in EP 244,839 and EP 939,700 in the name of the Applicant, herein incorporated by reference, wherein the obtainment of the functional products is also indicated.
To obtain non peroxidic products without chain scission, the peroxidic perfluoropolyethers are subjected to a thermal treatment at temperatures generally in the range 150xc2x0 C. and 250xc2x0 C., or to a photochemical treatment at temperatures generally in the range xe2x88x9240xc2x0 C. and +150xc2x0 C. in the presence of UV radiations having a wave length in the range 2,000-6,000 Axc2x0 and in the presence of an optional solvent. By fluorination of the so obtained products, products having formula (III) wherein h=0 and the T end groups are CF2X or C3F7 as above mentioned, are obtained.
The obtained products can be subjected to conversion in ionic form of the pendent fluorosulphonic groups xe2x80x94OCF2CF2SO2F. The conversion requires alkaline hydrolysis to obtain the xe2x80x94OCF2CF2SO3M wherein M is selected from Na, K, NR4 (Rxe2x95x90H, CH3, C2H5), and optional subsequent acid hydrolysis to obtain the xe2x80x94OCF2CF2SO3H. Preferably this conversion treatment is carried out on the products of the invention not containing peroxidic oxygen; said conversion in ionic form is described in U.S. Pat. No. 4,940,525.
The perfluoropolyethers of the invention are therefore transformable in the xe2x80x94OCF2CF2SO3H form and they result to have an high thermal stability (higher than 350xc2x0 C.) and a high acidity wherefore they can be used in very aggressive environments in the ionic conductivity field and in the ion exchange and as xe2x80x9csuperacidsxe2x80x9d in the catalysis field.
The solid polymers with main chain Cxe2x80x94C and pending groups xe2x80x94OCF2CF2SO2F and derivatives, are poorly soluble in apolar solvents. On the contrary the functional perfluoropolyethers of the invention are characterized by the absence of crystallinity and lower glass transition, as well as by high solubility in apolar solvents and in aqueous medium.
It is to be noticed that by carrying out the oxidative polymerization on the pure functional monomer, perfluoropolyethers having a very high concentration of functional sulphonic groups, unobtainable with any other synthesis method known so far, are obtained.
Due to their high chemical inertia, the products of the invention can also have other uses as catalysts or catalyst supports containing as catalytically active part particular functional groups or metal cations fixed by ionic exchange.
Another use of the perfluoropolyethers of the invention is the use as surface modifiers for polymeric and inorganic materials.